Actually the MACOs were more advanced than Starfleet (Archer says so in Harbinger) and it would not have been any more effort to transport them to Vulcan to handle the embassy security. Since the MACOs are Earth's genuine military that admits it's military, one really has to wonder why they aren't handling the duty that's always a military's, and why that job is being handled by the "explorers" instead.
Actually, while their costumes were obviously re-used Starfleet uniforms, their patches identified the embassy personnel as United Earth Diplomatic Corps and their ranks included that of corporal, which Starfleet doesn't seem to use (in contrast to the MACOs). No one ever actually refers to them as Starfleet personnel, despite the similarity of uniforms that would naturally cause the casual viewer to think that. They could be the equivalent of today's
Diplomatic Security Service, which is civilian. (Although, there are the military name and rank...but then Starfleet itself and many paramilitary organizations today use those as well.)
For what other reason is a ship going to be designed "for combat?"
While this is certainly an exercise in hair splitting—and as I've said I agree that by the 24th century Starfleet has
long had a military role, at least insofar as we would define it today—Paris puns that
Voyager was designed for "combat performance" over "musical performance" when Harry complains (or rather others do) that the fluid conduits in the walls conduct sound too readily. If one wants to get overly semantic (or pedantic) this
could mean little more than that the ship's structure was designed to withstand the pressures of combat as it might arise in emergencies, to hold up under attack, rather being designed for the intended purpose of fighting. Personally, I am content to take it at face value and believe combat was indeed one of the ship's intended purposes, though. After all, their original assignment was to chase down Maquis!
While watching TOS, especially season 1 it is very clear the writers were basing Starfleet on the US Navy, to the extent it can reasonably be called the Navy in Space. The references to it being non-military in the other shows come from Roddenberry suddenly feeling military to be a dirty word in his later years, and then for some reason Berman and now Abrams are sticking to that, despite the fact most of Roddenberry's other sacred cows have since been done away with.
It was more based on the Royal Navy in the early 19th century as depicted through the fictional Horatio Hornblower stories, to be accurate. And just for the record, speaking only for myself, I do not consider
military a "dirty word" and none of
my arguments on this subject are motivated by such a viewpoint, irrespective of whether or not it was Roddenberry's at any point. (Of course, it is surely worth at least
considering what the intent behind the fiction was, as you have.)
So, Starfleet builds ships that are purposely designed to be the ships to be used in war, but they don't build "warships."
This is certainly true by the end of the 23rd century, and indeed in all probability by the end of the 22nd. But what evidence exactly do we have that at the time of Starfleet's
founding its ships were "purposely designed to be the ships used in war," war being something which had been unknown on Earth—and in Earth space as well by the available references, probably thanks in no small part to the Vulcan High Command's presence, which might obviate the need and/or legal capacity for a dedicated space military in the eyes of Earth's government—for at least two decades prior?
Similar to America used to have a War Department, but changed the name to the Defense Department. But it had the same people, same uniforms, same (war) ships.
True, but go back far enough and we had barely if any defined military forces at all, only what could be scraped together
ad hoc, and relying heavily on civilian militias.
Since specific comparisons to the
U.S. Navy and
Coast Guard have been raised by others, let's review the early history of those. During the Revolutionary War the
Continental Navy (whose authorization was met with staunch vocal objection in the Continental Congress to begin with) initially consisted of a few converted merchant ships, later joined by 13 newly-constructed frigates, and eventually other vessels that were chartered/loaned/captured, only a handful of which survived the war, following which the entire operation was disbanded and they were sold off.
We were then entirely without a navy for years, relying solely on the
Revenue Cutter Service (which would eventually be merged with the
Life-Saving Service to form the Coast Guard, to be joined later still by the
Lighthouse Service and
Navigation and Steamboat Services) until it became clear that this was insufficient to deal with the threat of piracy that grew in the absence of the British Royal Navy's protection of shipping, and despite continued opposition in Congress, a U.S. Navy was authorized in 1794, with its first vessel to be launched being
U.S.S. Constitution (
) in 1797.
However we come to the exploratory nature of Starfleet and how that sits with regard to the question. In my view it has no bearing at all. The Beagle, famed for acting as a home for Charles Darwin whilst forming much of his theories, was a fully commissioned Royal Navy vessel, ie a military ship as were the Providence, the Discovery and frankly a vastly overwhelming number of historical vessels notably involved in exploratory or scientific work. Arguably in fact navies spend far more time and resources on exploration than they do fighting wars, in any era. That does not stop them being "military".
In other words the exploratory nature of the mission has no bearing on whether the organisation is a "military" as historically military navies focus much of their peacetime activities on exploration. It's simply something navies do, as in fact do armies to a lesser extent.
Despite the indisputable and amply evident fact that it's "something they do" I am not aware of
any historical military organization whose
stated primary purpose for existing was exploration, though. They exist to defend territorial interests and fight wars, and the exploration they carry out and participate in is incidental to this purpose. Conversely, it seems to me that
up to Archer's time at least, Starfleet existed to explore and seek out new life, and any participation in defense and fighting they undertook was incidental to
this purpose. The fact that their ships were well-armed and their organizational structure superficially based upon that of a navy (no doubt due to the similar need for discipline that Malcolm points out in "Singularity") does not in itself constitute strong evidence against this.
Also, it's worth noting that while its initial impetus certainly had military motivations and it has been facilitated by extensive backing and use of military resources, the exploration of
space specifically has been largely undertaken by civilian agencies in recent history.
OTOH, "military" being the opposite of "navy" is solid military terminology, again from about a century back. It has simply gone out of fashion; Trek could have it back with a vengeance.
If I recall, a few hundred years ago, the navy was not part of the "
Military", as the "Military" was the Army (soldiers and soldiering, which you don't do while sailing). The Navy was the Navy.
Starfleet might operate along a similar line of reasoning in definitions by the 24th century.
As in MACOs are military as they are ground forces?
Well, that
specific distinction is clearly not in play, as Malcolm describes the Royal Navy as military. The idea that there is an
analogous distinction between what Starfleet is and what "militaries" are is a better one, which I take it may be what one or more of you meant. (
I.e., space-based vs. planet-based instead of water-based vs. land-based.) And yet, I can't recall any examples of another world's space force being referred to as "the
x-ian starfleet," while I do seem to have some vague recollection of them being referred to as their militaries.
Wrong forum!
There are plenty of ways that the novel design and operation of the safety mechanism might prove confusing without it being necessary or sensible to posit that the former weapons had no safety mechanism whatsoever.
) reminiscent of Terra 10 from "The Terratin Incident"—but the line was "two hundred years" rather than "two centuries," which might have been a tad more fudge-able, yet even then I can't see how one would arrive at that phrasing when discussing a period ending only midway or more through the preceding century. I can see 180 years being rounded to 200 for example, but not by any stretch 115, and I could even see an event as late as 2099 being described as happening "two centuries" ago from the standpoint of 2270, but not one so late as 2154. (You may no doubt suggest that Sulu was just egregiously bad at dates, but that'd be cheating! 
) And besides, none of the specific details discussed in "The Slaver Weapon" match anything we see on ENT. And wait, feline Xindi now?
